1. Field of the Invention
The present invention relates to a secondary battery including a hydroxide-ion-conductive ceramic separator.
2. Description of the Related Art
Zinc secondary batteries, such as nickel-zinc secondary batteries and zinc-air secondary batteries, have been developed and studied over many years. Unfortunately, these batteries have not yet been put into practice. This is due to a problem that zinc contained in the negative electrode forms dendritic crystals, i.e. dendrites, during a charge mode of the battery and the dendrites break the separator to cause short circuit between the negative electrode and the positive electrode. Thus, a strong demand has arisen for a technique for preventing the short circuit caused by dendritic zinc in zinc secondary batteries, such as nickel-zinc secondary batteries and zinc-air secondary batteries.
In order to meet such a demand, batteries including hydroxide-ion-conductive ceramic separators have been proposed. For example, Patent Document 1 (WO2013/118561) discloses a nickel-zinc secondary battery including a separator composed of a hydroxide-ion-conductive inorganic solid electrolyte between a positive electrode and a negative electrode for preventing the short circuit caused by dendritic zinc, wherein the inorganic solid electrolyte is a layered double hydroxide (LDH) having a basic composition represented by the formula: M2+1−xM3+x(OH)2An−x/n.mH2O (wherein M2+ represents at least one type of divalent cation, M3+ represents at least one type of trivalent cation, An− represents an n-valent anion, n is an integer of 1 or more, and x is 0.1 to 0.4). Patent Document 2 (WO2013/073292) discloses a zinc-air secondary battery including a separator composed of a layered double hydroxide (LDH) having the same basic composition as that in Patent Document 1 and disposed on one surface of the air electrode for preventing a short circuit caused by dendritic zinc between the positive and negative electrodes during a charge mode of the battery and also preventing the intrusion of carbon dioxide into the electrolytic solution.
Patent Document 3 (WO2013/161516) discloses an application of a hydroxide-ion-conductive ceramic separator to a battery other than a zinc secondary battery; specifically, a lithium-air secondary battery including, as an anion exchanger, an inorganic solid electrolyte composed of a layered double hydroxide (LDH) having the aforementioned basic composition. According to this patent document, the anion exchanger can prevent the intrusion of carbon dioxide into the battery.